When you open a container of lubricating grease, chances are you may see a thin layer of oil at the top of the grease. The first thought that usually jumps to mind is whether the grease is suitable for use. The answer is in most instances, yes, but to understand the phenomenon of oil separation (bleeding) we need to revisit the fundamentals of grease.

Grease is a dispersion of a thickening agent in a liquid lubricant. the thickener can be compared to a ‘sponge’ that soaks up the lubricant. When the grease is subjected to stress or shear 9movement), the thickener releases the oil to provide the necessary lubrication. This is generally known as Dynamic Bleed. It is important that the grease has a controlled rate of bleeding during use to properly lubricate the bearing or component it has been placed in. The greater the amount of sheer stress encountered, the faster the grease thickener releases the oil. the thickener imparts little, if any, lubrication. If the thickener did not release the oil, the grease would be unable to perform its lubricating function.

In service, grease should also have a fair degree of reversibility after the stresses that have released the oil are relaxed. Reversibility can be described as the ability of the grease to recapture most of the oil and return to its original consistency when the equipment is shut down. The reversibility characteristics of grease are influenced by the type and amount of thickener used. The higher the thickener content, the greater the oil retention. As the base oil content is increased and the amount of thickener decreased, the forces that hold the oil also decrease, resulting in the base oil being loosely held in the thickener and easily separated.

Considering the above, one would think that using a higher thickener content is better. However, as mentioned earlier, grease with a thickener that does not release the oil readily, would be unable to perform its lubricating functions. It is therefore important that grease must have the proper balance of oil and thickener to function properly.The oil on top of grease in a container that has been opened for the first time is called Static Bleed. Static bleed, also referred to as oil puddling, occurs naturally for all types of grease and the rate of bleeding depends on the composition of the grease. Static oil bleeding is affected by:

• Storage Temperature
• Length of period in storage
• Vibrations the container may be exposed to during transport or storage
• Uneven grease surface in the container (the presence of high and low spots)

These conditions can cause weak stresses to be placed on the grease, resulting in the release of small amounts of oil and over time a puddle of oil can form on top of the grease. Reasonable static bleeding does not result in the grease being unsuitable for use. Any oil that has puddled on the grease can be removed by decanting the free oil from the surface or manually stirring it back into the grease. The quantity of oil that has separated from the grease is generally insignificant and represents a mere fraction of the total quantity of oil that is held in the thickener (typically less than 1%). This small amount of oil will not adversely affect the consistency of the remaining product and will have little or no effect on the performance of the grease.

In conclusion, it is therefore safe to say grease with puddling on the top is suitable for use subject to the following conditions:

• The amount of oil should be small, covering only low spots on the surface of the grease.
• The grease must readily absorb the oil upon stirring.

With winter approaching it is now an apt time to discuss the Pour Point of lubricants. The pour point of a lubricating oil can be described as the lowest temperature at which the lubricant will flow under specified laboratory conditions. It is often believed that the pour point of a lubricant is the lowest ambient temperature at which the lubricant can be used in a machine, but this is a fallacy.

At best an oil operating at an ambient temperature that is the same as the pour point of the oil, will merely churn at the oil pump until the churning causes an increase in the temperature of the oil. The increased temperature allows the oil’s viscosity to thin down sufficiently so that it slowly begins to flow through the oil passages to the lubricated components. This can take several minutes during which severe damage may be caused to various components due to oil starvation.

Most lubricating oils are still manufactured using paraffinic mineral base oil stocks. Virtually all these mineral base oils contain small amounts of dissolved wax. As the oil is cooled down, the wax begins to separate as crystals. When cooled down further, the wax crystals start to interlock to form a three-dimensional structure that traps the oil in small pockets within the wax structure. When this wax crystal structure becomes sufficiently rigid at low temperatures, the oil will no longer flow. ASTM D97 is the most frequently used test method to determine the pour point of petroleum products.

To improve (reduce) the pour point of these oils, pour point depressants (PPDs) are added. PPDs do not in any way affect the temperature at which wax crystallizes or the amount of wax that precipitates. They simply ‘coat’ the wax crystals preventing them to interlock and forming three-dimensional structures that inhibit oil flow. Good PPDs can lower the pour point by as much as 40 ⁰ C, depending on the molecular weight of the oil.

While the pour point of most oils is related to the crystallization of wax, certain oils, which are essentially wax free, such as polyalphaolefins (POAs), have viscosity-limited pour points. With these oils the viscosity becomes progressively higher as the temperature is lowered until no flow can be observed. The pour points of these oils cannot be lowered with PPDs. However, due to PAOs’ unique nature, they provide excellent low-temperature viscometrics and very low pour points that cannot be achieved by adding PPDs to mineral oil.

Just as important as pour point (if not more) is Cloud Point. The cloud point of an oil is the temperature at which a cloud of wax crystals start to appear when a sample is cooled under prescribed conditions. Below this temperature, the viscosity of the oil increases exponentially with decreasing temperature. This may well lead to oil pump cavitation in oil circulating systems, even before the pour point of the oil is reached — particularly in systems where the oil pump is positioned higher than the oil reservoir. ASTM D2500 is the most commonly used test method to determine the cloud point of petroleum products.

Considering all the above a good rule of thumb is that the pour point of a lubricating oil should be at least 1 O ^O C below the lowest anticipated ambient temperature. This will ensure dependable lubrication and better equipment reliability in the long term.

 

In response to OilChat #21 we have received requests to explain the different lubrication regimes (boundary, mixed and hydrodynamic) in more detail.

The regimes of lubrication can be compared to water skiing. Skiers normally start by entering the water with their skis on and holding onto the ski rope. When the skier is ready, the boat starts and the skis begin to move on the sand (boundary lubrication). As the boat accelerates, contact between the skis and sand is reduced (mixed lubrication). When the speed is sufficient, the skier rises out of the water with the front of the skis also out of the water and pointing upwards at an angle. It is this wedge profile between the skis and water that allows the skier to hydroplane on the water (hydrodynamic lubrication).

 

Before addressing lubrication regimes, we need to look at how friction and wear occur between moving machine surfaces. These surfaces appear smooth to the naked eye, but they are actually rough and uneven. Tiny peaks called asperities stick out and scrape against asperities on the opposing surface, causing friction and wear. The prime function of a lubricant is to prevent, or at least reduce, wear between surfaces moving on one another. We will endeavour to explain the lubrication of a plain journal bearing in parallel to the skiing analogy above. To enable the shaft to rotate in the bearing on the left, the diameter of the shaft must be less than the inside diameter of the bearing. This creates a wedge similar to the one between the skis and the water.

 

Boundary Lubrication is associated with metal-to-metal contact between moving surfaces. During start-up, the shaft and bearing asperities in a lubricated system will be in physical contact. The major portion of wear in any machine takes place in this regime. To prevent excessive wear within this regime, lubricants are formulated with additives to form a low-friction, protective layer on the wear surfaces. The base oil of the lubricant acts as a carrier to deposit the additives where they are needed. A suitable viscosity is important to ensure the oil can flow into tight spaces to lubricate the surfaces. The additive chemistry (anti-wear or extreme pressure) used within the lubricant is determined by the application.

Mixed lubrication is a transitional regime between the boundary and hydrodynamic lubrication, sharing characteristics of both. Oil molecules are cohesive as well as adhesive and cling to the shaft. As the shaft gains rotational speed, oil is carried into the wedge and starts to lift the shaft, but not sufficiently to separate the two surfaces completely. Mixed lubrication can also occur between surfaces where high loads are encountered, such as when reciprocating pistons slide against cylinder walls. With mixed lubrication, wear protection depends on both the lubricant viscosity, as well as the additives within the oil formulation. A lubricant with a too low viscosity will result in excessive metal-to-metal contact between the shaft and bearing.

Hydrodynamic lubrication (also known as full film lubrication) occurs when speed and load are such that the oil wedge between the shaft and bearing separates the surfaces completely. This is the ideal condition to avoid friction and wear. In fact, as long as this condition exists, no anti-wear or extreme pressure additives are required, and friction is so low that bearings can operate indefinitely without wear. Any friction remaining comes from the cohesiveness of the oil molecules as they slide past each other during operation. A lubricant with too high viscosity will result in an increase in the oil’s molecular friction. This will in turn increase operational temperatures and energy loss.

 

 

 

The lubrication regimes discussed above pertain to surfaces sliding against each other, such as journal bearings, reciprocating pistons, gears, thrust bearings, chains and guide bearings. In addition to this there is yet another lubrication regime:

Elastohydrodynamic lubrication is the condition that occurs when a lubricant is introduced between surfaces that are in rolling contact, such as roller bearings. As the oil enters the contact zone between the roller and raceway (by rolling action), the pressure that develops is sufficient to separate the roller and raceway completely. In fact, the pressure is high enough for the surfaces to deform elastically. The deformation only occurs in the contact zone, and the metal elastically returns to its normal form as the rotation continues, hence the term elastohydrodynamic lubrication. This lubrication regime may be compared to a car tyre aquaplaning on water. It occurs when water on the road accumulates in front of the tyre faster than the weight of the car can push push it out of the way.

The curve below shows the transition of the lubricating conditions between sliding surfaces. The vertical axis represents the coefficient of friction (an indication of the amount of friction) between sliding surfaces. The horizontal axis is a function of the relative speed between the two surfaces:

The curve clearly illustrates that the coefficient of friction is the highest when speeds are low and boundary conditions prevail.  Anti-wear and extreme pressure additives play an important role in this regime. The coefficient of friction is reduced dramatically as speed is increased in the mixed lubrication regime. Once hydrodynamic lubrication is reached, the coefficient of friction is at its minimum. This is because there is no longer any physical contact between the two surfaces owing to the fluid film carrying the entire load. The remaining frictional force is due to the internal friction of the fluid (we mentioned earlier oil molecules are cohesive). When the sliding speed increases further, the coefficient of friction rises again owing to drag (increase in viscous resistance). If the equipment constantly operates in this condition, the viscosity of the oil being used should be reduced. it is therefore evident that oil viscosity is important in the hydrodynamic regime.

 

Please be aware that the above is a simplified explanation of lubrication regimes and it does not address factors such as Newtonian behaviour, pressure vector distribution, position of shaft in the bearing during the different regimes and bearing parameters.

The majority of compressors require some form of lubrication to operate efficiently and reliably for extended periods of time. Oil-free compressors, such as those used to supply air for human consumption (where it is absolutely essential that the compressed air must not contain even minute traces of oil) are, however, the exception to the rule. This newsletter deals with the lubrication requirements of the most widespread compressor types that were discussed in OilChat #20.

Reciprocating Piston Compressors

The lubrication requirements of these positive displacement compressors are in many instances the most demanding of all compressor types. Regardless of size and configuration, all reciprocating compressors have similar components to be lubricated. These are pistons, piston rings, cylinder walls, valves, crankcase bearings and cross head components (if fitted). It is particularly important that reciprocating compressor oils should provide adequate protection against wear and deposit formation. The piston ring and cylinder contact area experience all the different lubrication regimes (i.e. boundary, mixed, and hydrodynamic) during every stroke of the piston. Boundary lubrication conditions occur near the top and bottom dead centre when the piston slows down to change direction of travel. This requires some form of anti-wear protection. Exposure of the lubricating oil to hot oxidizing conditions can be severe in reciprocating compressors. Some oil oxidation is inevitable, particularly in the discharge valve area. Adherence of oxidized residues to hot valve surfaces can be minimized by including a stable detergent/dispersant in the lubricating oil. An ideal lubricating oil for reciprocating air compressors would be made from a well-refined stable base oil with ashless anti-wear additives and good high temperature detergents/dispersants, along with oxidation inhibitors, foam suppressants and rust inhibitors for protection during shutdown. Viscosity requirements of reciprocating compressors are in the ISO viscosity range 68 to 220, or even higher for very high pressure, high temperature machines.

Rotary Screw Compressors

These positive displacement compressors use two intermeshing screw-shaped rotors for compression. The two major sub-categories are wet and dry screws. Dry screw designs have timing gears to synchronize the screw movement. However, the most common type of screw compressor is the flooded or wet screw design where the primary (male) rotor drives the secondary (female) rotor. In oil-flooded screw compressors the lubricant is injected into the air being compressed. The oil provides a lubricating and sealing film between the two screws. With these compressors the air and oil must be separated after compression. The major functions of the lubricant are to cool, seal, prevent rust and lubricate the bearings, rotors and shaft seals. In oil-flooded screw compressors there is intimate contact between the air and the lubricant, causing great potential for oxidation and deposits. The lubrication requirements of these compressors are similar to that of reciprocating compressors, except that the anti-wear requirements of screw compressors are not quite as demanding as reciprocating compressors. Viscosity requirements of screw compressors are in the ISO viscosity 32, 46, 68 or 100 range. Oil-flooded screw compressors are the main compressor type used for air compression in industrial applications.

Rotary Vane Compressors

Rotary (sliding) vane compressors consist of a rotor with a number of blades (vanes) in slots in the rotor. The rotor is mounted offset in its housing. Centrifugal forces ensure that the vanes are always in close contact with the housing. These compressors are available in oil-lubricated or oil-less designs. The type depends on the application, duty-cycle, and maintenance preferences. With non-lubricated variants, you replace the vanes with every service. When servicing oil-lubricated rotary vane compressors you replace the oil, filter and maybe the oil separator. Lubrication requirements of oil-lubricated rotary vane compressors are similar to those of oil-flooded (wet) rotary screw compressors. Oil is injected into the air (flooded lubrication) to cool, seal and lubricate the vanes, bearings and endplates. Obviously an oxidation inhibited oil is required. Contact of oil with the air suggests that a foam inhibitor would be beneficial. A rust inhibitor will provide protection against rusting during shutdown and for intermittent operation. In addition, the oil should have good detergent/dispersant properties to maintain a deposit-free circulating system and prevent vane sticking. The vanes may make contact with the cylinder walls in a boundary lubrication condition; therefore anti-wear oils are often used, ranging in viscosity from ISO 46 tol 50, depending on the application.

in more detail in the next issue of OilChat.

Dynamic Compressors

Radial Centrifugal and Axial Flow compressors use very high speed spinning blades or impellers to compress the air. These compressors do not require internal lubrication, hence only rust and oxidation inhibited oils are commonly used to lubricate and cool the outboard bearings. Due to the high speed, relatively low viscosity oils are used. The lubricant generally recommended for dynamic compressors is highly refined rust and oxidation inhibited oil of ISO 32 viscosity grade. Where a gear driven speed increaser is used, an ISO 46 or even ISO 68 viscosity grade may be required.

The same types of compressors that are used for air are also used for gases. Hydrocarbon based lubricants, mineral and synthetic (PAO), should NEVER be used for compressing active gases such as hydrogen, chloride, oxygen, etc. These gases may react chemically with hydrocarbon oils. Under pressure the chemical mixtures of these gases and hydrocarbon oil can be explosive. Lubricants blended with Group V base oils, normally polyalkylene glycol, should be used for gas compressors.

The choice of a compressor lubricant depends on the type and construction of the compressor, the gas being compressed, the degree of compression and the final outlet temperature. Most compressor manufacturers recommend lubricants that have been tested in their machines under controlled conditions. Make sure you are familiar with your manufacturers’ recommended lubricants, keep them in stock and adhere to the specified service intervals. If you don’t, your compressor may end up looking like this….

If you are in doubt our experts are at your disposal and ready to provide you with advice and answer any questions you may have. For more information, call 011 462 1829.

A compressor can be described as a pump or other device that ‘inhales’ air and delivers it at a higher pressure. Compressors are also used to compress a variety of gases. The very first air compressor was the human lung. To illustrate, we use compressed air from our lungs to inflate balloons. In the early days of mankind our ancestors used their breath to stoke fires and to increase the temperature of glowing coals. With the advent of the Metal Age more heat was required to melt metals, such as gold and copper, and circa 1 500 B.C. a basic type of air compressor, called bellows, was invented. This device was a hand-held, and later foot-operated, flexible bag made of animal skin, that produced a concentrated blast of air that was ideal for achieving higher temperature fires. In 1 762 during the early days of the Industrial Revolution John Smeaton, an innovative engineer, designed an air blowing cylinder driven by a water wheel. It soon replaced the bellows in many industrial applications.

Today compressors are generally driven by electric motors, turbines or internal combustion engines. Modern compressors come in many designs and sizes, ranging from small units at petrol stations to inflate car tyres, to massive industrial machines that are too large to fit into an average-sized garage. The air pressure in car tyres is usually between 2 and 3 bar (29.0 and 43.5 pounds per square inch). The latest high-performance compressors can deliver pressures well in excess of 70 bar (more than 1000 psi).

Lubrication plays a critical role in the efficient and reliable operation of compressors. However, before we look at compressor lubrication, we need to understand the design and operation of the most common types of compressors available on the market. Compressors are divided into two main categories: Positive Displacement and Dynamic Compressors. Following is a brief discussion of the most popular compressors within these categories:

Positive Displacement Compressors

These compressors work by filling a chamber with air. The volume of the chamber is then reduced and consequently, the pressure in the chamber is increased. By nature of their design, Positive Displacement Compressors can deliver very high pressures. The most common Positive Displacement Compressors are:

Reciprocating Piston

Reciprocating compressors function similarly to a car engine. A piston slides back and forth in a cylinder, which draws in and compresses the air, and then discharges it at a higher pressure. Reciprocating compressors are frequently multiple-stage systems, which means that one cylinder’s discharge will lead into the input side of the next cylinder. This allows for more compression than a single stage. Due to their relatively low cost, reciprocating compressors are probably the most commonly used compressors.

Rotary Screw

These compressors use two meshing screws (also called rotors) to compress the air. In oil flooded rotary screw compressors, lubricating oil bridges the space between the rotors. This provides a hydraulic seal and transfers mechanical energy between the driving rotor and the driven rotor. Air enters at the suction side, the meshing rotors force it through the compressor, and the compressed air exits at the end of the screws.

Rotary Sliding Vane

Rotary vane compressors consist of a rotor with a number of blades (vanes) inserted in radial slots in the rotor. The rotor is mounted offset in a housing. As the rotor turns, the blades slide in and out of the slots, keeping contact with the wall of the housing. Thus, a series of increasing and decreasing volumes are created by the rotating blades to compress the air. Centrifugal forces ensure that the vanes are always in close contact with the housing to form an effective seal.

Dynamic Compressors

Dynamic compressors use very high speed (up to 60,000 rpm) spinning blades or impellers to accelerate the air. The increased velocity causes an increase in air pressure. Dynamic Compressors deliver large volumes of air but generally at lower pressures. The following designs are the most common types of Dynamic Compressors:

Radial Centrifugal

A rotating impeller in a shaped housing is used to force the air to the rim of the impeller, increasing the velocity of the air. A diffuser (divergent duct) section converts the velocity energy to pressure energy. Radial compressors are primarily used to compress air and gasses in stationary industrial applications.

 

Axial Flow

These compressors use fanlike airfoils (also known as blades or vanes) to compress air or gas. The airfoils are set in rows, usually as pairs, one rotating and one stationary. The rotating airfoils (rotors) accelerate the air. The stationary airfoils (stators) redirect the flow direction, preparing it for the rotor blades of the next stage. Axial compressors are normally used where very high flow rates are required. By nature of their design, axial flow compressors are almost always multi-stage.

The majority of compressors requires some form of lubrication to either cool, seal or minimize wear of their internal components. Many compressors are adequately lubricated by premium-grade turbine oils. We will address the specific lubrication requirements of the above compressors in more detail in the next issue of OilChat.

Since the first ACEA (European Automobile Manufacturers’ Association) Oil Sequences were introduced in 1996, updated specifications were issued in 1998, 1999, 2002, 2004, 2007, 2008, 2010 and 2012- please refer to OilChat numbers 11 and 12. The long awaited next issue of the ACEA Oil sequences was finally released during December 2016. Reasons for this delay were the replacement of obsolete tests with new ones to reflect engine technology advancements and also to address the complications associated with the increase in use of biofuels.

The ACEA Oil sequence comprises of three classes: one for Petrol and Light Duty Diesel engines, one specifically for Petrol and Light Duty Diesel engines with exhaust after treatment devices and one for Heavy Duty Diesel engines. The ACEA sequences make up some of the industry’s most important performance standards and the ACEA 2016 update is a significant step for the global lubricant industry. ACEA 2016 sets a substantial increase in required performance from ACEA 2012.

ACEA 2016 Changes compared to ACEA 2012

The main features of the new ACEA 2016 engine oil sequences are the optimized performance capabilities in relation to the latest engine technologies, compatibility with new elastomer materials (seals, hoses etc.), improved compatibility with biofuels and increased potential to reduce fuel consumption. Some additional tests were also introduced for the individual categories.

ACEA 2016 Specific Changes

• Category A1/B1 has been removed and not replaced.
• Category C5 has been introduced to address the reduction of CO² levels and fuel consumption.
• Introduction of various new engine tests:
• CEC L-107 sludge test has not yet been finalized. In the interim Daimler’s sludge test is being used.
• CEC L-111 petrol direct injection test for piston cleanliness and deposits in turbochargers.
• CEC L-109 oxidation test for engine oils used with biodiesel.
• CEC L-106 oil dispersion test at moderate temperatures for diesel direct fuel injection engines.
• CEC L-112 test to check oil/elastomer capability.
• CEC L-104 engine oil performance test to measure the effects of biodiesel using the DC OM646 DE22LA engine for piston cleanliness and sludge.

The ACEA 2016 Oil Sequence comprise the following twelve different Performance Categories within the three Service Classes:

A/B: Petrol and Light Duty Diesel Engine Oils (High SAPS)

A3/B3, A3/B4 & A5/B5

C: Catalyst Compatible Petrol and Light Duty Diesel Engine Oils (Low SAPS)

C1, C2, C3, C4, C5

E: Heavy Duty Diesel Engine Oils

E4, E6, E7, E9-

The table below summarises the changes that have occurred for each of the ACEA Oil Sequences since 1996:

	ACEA 1996	ACEA 1998	ACEA 1999	ACEA 2002	ACEA 2004	ACEA 2007	ACEA 2008	ACEA 2010	ACEA 2012	ACEA 2016
A	A1-96	A1-98	A1-98	A1-02	–	–	–	–	–	–
	A2-96	A2-96 #2	A2-96 #2	A2-96 #3	–	–	–	–	–	–
	A3-96	A3-98	A3-98	A3-02	A1/B1-04	A1/B1-04	A1/B1-08	A1/B1-10	A1/B1-12	–
	–	–	–	A5-02	A3/B3-04	A3/B3-04	A3/B3-08	A3/B3-10	A1/B3-12	A3/B3-16
B	B1-96	B1-98	B1-98	B1-02	A3/B4-04	A3/B4-04	A3/B4-08	A3/B4-10	A3/B4-12	A3/B4-16
	B2-96	B2-98	B2-98	B2-98 #2	A5/B5-04	A5/B5-04	A5/B5-08	A5/B5-10	A5/B5-12	A5/B5-16
	B3-96	B3-98	B3-98	B3-98 #2	–	–	–	–	–	–
	–	B4-98	B4-98	B4-02	–	–	–	–	–	–
	–	–	–	B5-02	–	–	–	–	–	–
C	–	–	–	–	C1-04	C1-04	C1-08	C1-10	C1-12	C1-16
	–	–	–	–	C2-04	C2-04	C2-08	C2-10	C2-12	C2-16
	–	–	–	–	C3-04	C3-07	C3-08	C3-10	C3-12	C3-16
	–	–	–	–	–	C4-07	C4-08	C4-10	C4-12	C4-16
	–	–	–	–	–	–	–	–	–	C5-16
E	E1-96	E1-96#2	–	–	–	–	–	–	–	–
	E2-96	E2-96#2	E2-96#3	E2-96#3	E2-96#5	E2-96#5	–	–	–	–
	E3-96	E3-96#2	E3-96#3	E3-96#3	–	–	–	–	–	–
	–	E4-98	E4-99	E4-99	E4-99#3	E4-07	E4-08	E4-08#2	E4-12	E4-16
	–	–	E5-99	E5-99	–	–	–	–	–	–
	–	–	–	–	E6-04	E6-04#2	E6-08	E6-08#2	E6-12	E6-16
	–	–	–	–	E7-04	E7-04#2	E7-08	E7-08#2	E7-12	E7-16
	–	–	–	–	–	–	E9-08	E9-08#2	E9-12	E9-16

ACEA internationally omitted “E8” from the Sequences.

 

Each new issue of the Oil Sequences may include a new sequence, an increase in severity for an existing sequence or a change in testing with no change in severity. the nomenclature used by ACEA as a suffic to the Category, depends upon the type of change.

The complete ACEA 2016 Oil Sequences Requirements and Test Methods are available on http://www.acea.be/uploads/news documents/ACEA European oil sequences 2016.pdf

In this issue of OilChat we will endeavour to clear some of the fallacies surrounding Flash Point. It is often believed that the Flash Point of a volatile liquid is the temperature at which the liquid will ignite (start to burn) spontaneously without an ignition source. This however is not true. Flash Point is defined as the lowest temperature at which a liquid (usually a petroleum product) will form a vapour in the air near its surface that will “flash, ” or briefly ignite, on exposure to an open flame.

Flash Point is an indication of the flammability or combustibility of a substance. The lower the Flash Point, the greater the fire hazard. The use of the Flash Point as a measure of the hazardousness of petroleum products dates back to the 1 9th century. Before the advent of automobiles, paraffin was the most sought after petroleum product which was primarily used as fuel for lamps and stoves. At the time there was a tendency by petroleum distillers to leave as much as possible of the commercially ‘worthless’ petrol in the paraffin in order to produce more product. This adulteration of paraffin with highly volatile petrol caused numerous fires and explosions in storage tanks and household appliances. In response legal measures were instituted to curb the danger, test methods were prescribed and minimum flash points were set.

You may well wonder why we sometimes find a variance when we compare the Flash Points of two similar products. The answer lies in the test method used. Flash points are measured by heating a liquid to specific temperatures under controlled conditions and then applying a flame to the vapour above the surface of the liquid. The test is done in either an “open cup” or a “closed cup” apparatus.

In the open cup test the sample is poured into a test cup that is completely open at the top. A thermometer is placed in the sample before it is heated. The test flame is passed over the cup at every 2 ⁰ C increase in the sample temperature. When the sample vapours ignite momentarily the Flash Point is reached. The most commonly used test method is the ASTM D92 Cleveland Open Cup (COC) test.

In the case of the closed cup test, the sample is placed in a test cup with a sealed lid that opens when the ignition source (flame) is applied. The closed cup traps all the vapours that are generated during the heating of the sample and the vapours are not exposed to the atmosphere as they are in the open cup method. It is therefore no surprise that the closed cup test yields lower Flash Points than the open cup test. The ASTM D93 Pensky-Martens Closed Cup (PMCC) test is normally used to determine closed cup Flash Points. There is no set conversion factor for these Flash Point tests but PMCC is generally 5 ⁰ C to 1 SC lower than COC for lubricating oils.

Flash Point is often used as a descriptive characteristic of petroleum products, and it is also used to help portray the fire hazards of liquids. It refers to both flammable and combustible liquids. There are various standards for defining each term but it is generally agreed that:

• liquids with a PMCC Flash Point less than 37.8 ⁰ C are flammable, and
• liquids with a PMCC Flash Point higher than 37.8 ⁰ C are combustible.

Although Flash Point primarily characterizes the fire hazards of liquids, it can also be an indicator of the quality of the base oils used in lubricants. In days gone by Flash Point was not really an issue but since the introduction of lower viscosity oils, such as SAE 5W-40 and even SAE OW-30, it became a more important consideration. The thinner the oil, the lower the Flash Point and the greater the tendency for the oil to suffer vapourisation loss at elevated temperatures. This results in the oil to burn off on hot cylinder walls and pistons in engines and thereby increasing oil consumption. A PMCC Flash Point of 200⁰ C is generally recognised as the minimum Flash Point for engine oil to prevent possible increased oil consumption at high operating temperatures.

If the open cup test is continued at increased temperatures after the Flash Point is attained, a point may be reached where the vapour continues to burn after being ignited. When the sample vapour sustains combustion, the Fire Point is reached. The Fire Point of a liquid can therefore be defined as the lowest temperature at which the vapour continues to burn (for at least five seconds) after being ignited by an open flame. The Fire Point for petroleum products is seldom listed, while Flash Point appears on most product data sheets. Generally, the Fire Point is about 1 O ^O C higher than the Flash Point, but if the value must be known, it should be determined experimentally. It should be noted that Fire Point testing is not undertaken in closed cup apparatus.

What many people perceive to be the Flash Point is actually the Auto-Ignition Temperature. Unlike with Flash Point and Fire Point, the Auto-Ignition Temperature does not need an ignition source. The Auto-Ignition Temperature of a substance is the lowest temperature at which it will ignite spontaneously in a normal atmosphere without an external source of ignition, such as a flame or spark. The Auto-Ignition Temperature (also known as Kindling Point) is a much higher temperature than the Flash Point and Fire Point.

Leading automotive, industrial and energy solutions manufacturer Q8Oils – a subsidiary of oil giant Kuwait Petroleum Corporation – has signed a distribution and manufacturing license agreement with South Africa-based Blue Chip Lubricants Pty Limited. Based in Randburg, Blue Chip’s role as sole importer and distributor of Q8 lubricants in South Africa will also see the company manufacture locally to ensure they can deliver a high level of service and flexibility to their customers.

Commenting for Blue Chip, director Gary Marais says: “All products manufactured locally will be blended under strict Q8Oils quality controls, using its own high-quality base oils and additives. In addition, the formulations we use are the same as those used by Q8Oils customers in Europe and North America.”

Established in 1983, Blue Chip Lubricants is a leading independent manufacturer, marketer and distributor of a wide variety of high-quality lubricants and greases in South Africa; and has gained a reputation for the production of reliable products and services.

Championing the partnership, Q8Oils regional sales manager Abdulmohsen Homoud says: “When choosing a partner for this region it was essential that we found a high-quality blender and a ‘can do’ partner, both technically and commercially. The Q8Oils and Blue Chip partnership is a perfect fit for the South African market, with customers being the ultimate winners.”

He goes on to say that, with Q8Oils’ marketing, manufacturing and research headquarters remaining in Europe, Blue Chip has significant corporate resources to call on whenever they are required.

This is not an optical illusion.

Tractors don’t come up on our radar screens all that often but modern farm equipment is a far cry from the “mechanical plow horses” of yesteryear. These new machines may still not break any speed record, but space technology is now being incorporated into agricultural equipment in the form of GPS devices, onboard computers, auto-steer system and even driverless technology!

Notwithstanding this array of state-of-the-art gizmos, lubrication still plays a critical role in the efficient and reliable operation of agricultural machinery. Tractors and other farm equipment, such as combined harvesters, have various components that need to be lubricated. These include the engine, transmission, final drives, oil immersed ( wet ) brakes hydraulic system and the power take-off ( PTO ). Just imagine the cost consequences if farmers had to stock different oils for all these applications. Furthermore, with so many lubricants in the oil store, there is also the risk of using the wrong oil for a specific component. It is therefore no wonder that agricultural equipment manufacturers and oil companies have worked together to come up with multifunctional lubricants:

Super Tractor Oil Universal (STOU/SUTO)

These oils fulfill several roles and make machine maintenance much simpler. They also reduce the number of lubricants farmers need to keep around because they can generally be used for all the applications mentioned above. When you peruse the product data sheet of a reputable STOU you will find that it meets the requirements of a host of Industry and Equipment Manufacturers’ (OEM) specifications. These may include, but are not limited to, the following:

• Engines: API CG-4/SF
• Gears: AP GL-4
• Transmissions: ZF TE-ML 06A / 06B / 06C / 06G
• Wet Brakes: Case MS 1317
• Hydraulics: Eaton Vickers M-2950-S.

A STOU fluid can be described as a general-purpose farm lubricant with reasonable engine performance, fair load carrying capacity for gears and moderate hydraulic oil performance. However, as engines become more demanding, transmissions more sophisticated and hydraulic system pressures higher, trying to meet all the requirements with one fluid becomes more complicated. For instance, if a manufacturer recommends an API CI-4 performance level oil for the engine, two separate lubricants may have to be used since it is unrealistic to expect a single oil to meet API CI-4 and all the other service categories mentioned above. In such an instance it would be advisable to use a dedicated engine oil and a higher performance multifunctional lubricant for the other components.

Universal Tractor Transmission Oil ( UTTO )

These lubricants are also referred to as Tractor Hydraulic Fluid ( THF ) or Transmission, Differential and Hydraulic ( TDH ) fluid. They are used where the equipment manufacturer recommends a separate engine oil. UTTOshave no engine oil credentials, better hydraulic oil performance and improved wet brake fluid characteristics.

When you compare STOU and UTTO product data sheets you may well find they have some transmission, rear axle, wet brake and hydraulic oil specifications in common. However high-performance UTTOs will boast with OEM specifications that are unlikely to be met by STOUs such as:

• Case MS 1207: Hy-Tran Plus, transmissions, hydraulics, wet brakes
• Massey Ferguson CMS M 1141: Transmissions, hydraulics, highly loaded wet brakes
• Volvo 97302-10: Transmission with built in wet brakes

As tractors become more sophisticated and require higher quality oils for satisfactory performance, there will most likely be an increased trend away from the all-purpose STOU fluid to a specific engine oil and UTTO combination.

TO-4 Fluid

UTTOs should not be confused with TO-4 fluids. UTTOs are mainly used in agricultural applications, although they are sometimes recommended for construction machines, such as Bell ATDs. TO-4 fluid originates from the Caterpillar TO-4 ‘Transmission Oil’ specification. TO-4 has become a standard term used within the industry for a specific type of additive/ fluid. TO-4 fluids normally meet Allison C4and other OEMrequirements as well.

Although both UTTOs and TO-4 fluids are designed for wet brake applications, they are not interchangeable since they have different frictional properties.Construction machinery, for which TO-4 fluids are intended, is normally much bigger and heavier than agricultural equipment. A higher level of friction is required to ensure that these heavy machines can stop on steep slopes, such as access roads down open cast mines.Tractor size, and therefore weight, is limited, as they need to use public roads, and therefore less friction is required to stop agricultural equipment. This results in TO-4 fluids having a higher coefficient of friction than UTTOs. Using the wrong fluid will mean that fluid/brake surface interaction will be affected and thereby reducing braking efficiency with possible catastrophic results.

Conclusion

Know your equipment manufacturer’s recommended lubricants, have them on hand and pay attention to tractor and equipment service intervals. If in doubt our experts are at your disposal, ready to provide you with advice and to answer any of your questions. For more information, please visit www.bcl.q8oils.co.za